The present invention relates to insulating materials used in pollution control devices and more particularly to a method for making a preform from an intumescent or a non-intumescent sheet material for use as an insulating end cone in pollution control devices and the resulting preform insulating end cones.
Pollution control devices such as catalytic converters and diesel particulate filters or traps are well known, and are most typically used to purify the exhaust gasses produced by internal combustion engines. These types of pollution control devices typically comprise a metal housing with a monolithic element securely mounted within the casing by a resilient and flexible mounting mat.
Two types of devices are currently in wide spread use—catalytic converters and diesel particulate filters or traps. Catalytic converters contain a catalyst, which is typically coated on a monolithic structure mounted in the converter. Monolithic structures are typically ceramic, although metal monoliths have been used. The catalyst oxidizes carbon monoxide and hydrocarbons, and reduces the oxides of nitrogen in automobile exhaust gases to control atmospheric pollution. Diesel particulate filters or traps are wall-flow filters which have honeycombed monolithic structures typically made from porous crystalline ceramic materials. Alternate cells of the honeycombed structure are typically plugged such that exhaust gas enters one cell and is forced through the porous wall of one cell and exits the structure through another cell.
Due to the relatively high temperatures encountered in pollution control devices, it is important that the device be well insulated. Insulation is typically provided by securely mounting the monolithic element within the casing using an insulating mounting mat comprised of a suitable material. In addition, inlet and outlet end cone assemblies which provide a transition from the exhaust pipe to the pollution control device can also be insulated. The inlet and outlet end cone assemblies can be insulated by providing a double-walled end cone assembly comprising an outer metal housing and an inner metal housing, with a gap defined between the inner and outer cone housings. Typical insulating liners are die cut from flat intumescent or non-intumescent sheet materials which then have to be manually wrapped or stuffed between metallic end cone housings. The die cut flat sheet materials may or may not have cuts so to prevent buckling of the material when the flat sheet material is placed between end cone housings.